Holes in cabin air filter

I changed my Gen II cabin filter every 10,000 miles. The filter was dirty with some debris, but never any holes. Sounds like you may have a visitor that found a home in your car for the winter.

 

Most likely mice. See boo's post below for very helpful pointers on screening, which may reduce the problem.

 

If appropriately sized debris of an appropriate material were introduced, yeah, it's possible. I don't think it's likely, though. You'd have heard any such debris moving around the system.

 

You can screen-off the largest and most likely entrance holes for mice and other rodents. The holes are under the windshield wipers and plastic cowl on the bottom of the windshield.

This file has the best easy-to-follow instructions and pictures for removing the windshield wipers and cowl:

BT Tech Strut Tower Brace Install - By GadgetDad (Lee) v2.doc

After you remove the wipers and cowl, you can screen-off the several small and large openings to help prevent mice from entering the cabin. Mice have been known to especially like building homes in the cabin filter area.

I had to remove the wipers and cowl when I was installing my strut tower brace. While the wipers and cowl were removed I decided to do a quick and dirty screening job using what I had readily available which were vinyl double-screened gutter guards and tape (the best or better screening job would use metal screens and screws). Here's a pic:



And here's the thread with pictures showing the best or better way to screen-off the openings in both the front and the rear hatch areas, using 1/4 inch metal screens and self-tapping screws:

http://priuschat.com/forums/knowledge-base-articles-discussion/51005-mouseproofing-prius.html

 

The world's small rodents take a dim view of this type of Prius mod, and they will stick you with bubonic plague or Hantavirus if given a chance. So watch it.

 

Even worse, they will never let you become a Disney star.